The wolf tone resonator (killer) is for mounting under the top of the cello (near left F-hole), so that it is not visible. An extensive user manual is included for this. For the (glued) mounting, a C-clamp is required that presses the resonator until the glue has dried. The following three versions are available:

*Es-F (middle sound range)
* DE (low range)
* E-Fis (high sound range)